1. Field of the Invention
The present invention relates to polyisocyanate-based resins containing modified hydrazide groups, to one-component, thermoset compositions containing these resins and a cross-linking component and to their use for the production of coatings, sealants and adhesives.
2. Description of the Prior Art
One-component polyurethane coating compositions derived from blocked polyisocyanates and polyols are an important class of materials for applications such as automotive OEM coatings. These one-component compositions are used because of the difficulties encountered when using two-component coating compositions in industrial applications. In the two-component compositions the polyisocyanates are not blocked, which results in several disadvantages. The two-component compositions must be accurately mixed or the properties of the resulting coatings can be substantially affected. In addition, after the components are mixed they have a limited pot life since the components continue to react until an unusable solid is obtained.
These disadvantages are not present in one-component coating compositions containing polyols and polyisocyanates blocked with reversible, monofunctional blocking agents for isocyanate groups. However, there are also disadvantages with one-component coating compositions, which are primarily caused by the volatilization of the blocking agent. The release of the blocking agent can cause blistering and yellowing in thick films and oven fouling. In addition, the blocking agents are considered to be volatile organic compounds (VOC's) in the same manner as organic solvents. Therefore, certain coating compositions may not satisfy environmental regulations solely due to the presence of blocking agents.
It is an object of the present invention to overcome the known disadvantages of one-component coating compositions caused by the release of blocking agents during cure without affecting the advantages of these coating compositions when compared to two-component coating compositions. It is an additional object of the present invention to be able to obtain coatings that possess chemical stability, including acid etch resistance, which is comparable to that obtained from coatings prepared using blocked polyisocyanates as the crosslinking agent.
These objects can be achieved with the one-component compositions according to the present invention. These compositions do not require blocking agents and, thus, do not release blocking agents. When the coating compositions according to the invention are cured, the only compounds released are water or monoalcohols, which are much less toxic than conventional blocking agents.